Electric discharge devices



April 8, 1958 w. J. SCOTT ELECTRIC DISCHARGE DEVICES Filed Jan. 7, 1955 l/VVE/V 7'01? WILL/19M JOSEPH pea ELECTRIC DISCHARGE DEVICES William Joseph Scott, -Rugby, England, assignor to The British T mSon-Houston Company Limited, a British company Application January 7, 1955, Serial No. 480,519 Claims priority, application GreatBritain January 8, 1954 3 Claims. (Cl. 315-41) This invention relates 'to'electric discharge devices of the kind in which a discharge, intended to occur between two main electrodes in an ionisable medium under desired conditions, is stimulated by means of a conditioning or priming discharge between one of the main electrodes and 'an auxiliary or prime'relectrode to which a potential with respect to-that-main electrode is applied during operation.

According to the invention the auxiliary electrode is constructed to incorporate a resistor which is in series with and close to the auxiliary discharge path in order to. stabilize the auxiliary :discharge.

One type of electric discharge device to which the invention is applicable is that known as a transmit-receive (T. R.) cell employed in radar systems :for protecting the receiving apparatus from the energy of the transmitter, the transmitter and receiver being connected to a common aerial system. In a device of this character, a discharge is intended-to occur (when the transmitter is producing energy lpulses). between electrodes which form part of a tuned =circuit resonant at or near the frequency of the transmitter :energy, the electrodes being spaced apart in an evacuated chamber filled with an ionizable medium, such as argon containing a. trace of water vapour. In one knownarrangement, the auxiliary electrode is in the form of a conductor substantially completely shielded by one of the main electrodes from the other main electrode and is also shielded from the main electrode with which it is associated by a sleeve of vitreous material surrounding the auxiliaryel'ectrode. In one construction, the. vitreous material is sealed on to the outer periphery of the auxiliary electrode so as to expose only the tip thereof.

In carrying out the invention in connection with a' T. R. cell of this character, the resistance is inserted within the vitreous sleeve so that the path taken by the current flowing from the auxiliary electrode to the main electrode with which it is associated, includes the resistance.

It is preferable, however, to substitute for an intermediate portion of the conductor forming the auxiliary electrode a rod of highly resistive material, such as a ceramic resistor. To this end, the major part of the auxiliary electrode may consist of a conductor consisting of a material to which glass may readily be sealed, e. g. an iron-nickel-cobalt alloy, such as Nilo K. The resistor bar is attached to the end of the conductor, and to the remote end of the resistor bar is secured a small tip of metal, e. g. rhodium or copper, from which the discharge to the auxiliary electrode take place, the whole being enclosed within a sleeve of glass extending up to the tip of the electrode and sealed to the conductor at 2; of the electrode by reason of the shielding effect provided by the surrounding glass sleeve.

Alternative1y,the sleeve protecting the resistor bar and its connections to the adjacent parts of the auxiliary electrode may be constituted by a sleeve of insulating ma teri'al, such as Sintox registered trademark, the insulating sleeve being supported by being joined or sealed to the glass sleeve which surrounds and is sealed to the conductor. I

'In, the accompanying drawings, Figs. 1 and 2 show "respectively, in "side elevation and end view, a T. R. cell of known kind to which 'th'e present invention 'is applicable, while Figs. 3, 4 and 5 show in partial crosssection constructions of auxiliaryelectrode embodying the invention. a

Referring now to the known construction "of T. R. cell shown in Figs. 1 and 2, this consists of a short length of metal wave guide 1 of rectangular'cross-section having end flanges 2, 3, to enable it to be attached to similar flanges on wave guides extending in either direction from the T. R. cell. The cell is furnished with windows 4 at each end which'are of the same construction and which serve to seal the cell hermetically so that it may be evacuated or filled with a suitable gas and/or vapor. Each window comprises a rectangularmetal plate having a resonant slot 5 into which glass is sealed'by fusion, the slot being of such dimensions as to be tuned to preferably the mid frequency of the frequency band'over which the T. R. cell is to respond. Intermediate the windows 4 is a rectangular slot or iris 6 formed between the inner edges of two partitions 7 which extend between the opposite faces of the upper and lower longer walls of the guide. These are preferably formed by a single flange member the flanges of which are brazed to the inner faces of the walls'of the guide. The partitions are separated from the side walls of the guide by spaces 8 for the purpose of facilitating the chemical cleaning and/ or electroplating of the envelope during manufacture.

Between the inner edges of the partitions '7 are coaxially mounted on the lower and upper walls of the guide the main electrodes 11, 12. These constitute, with the iris 6, a resonant circuit tuned to substantially the same frequency as that to which the slots 5 are tuned. The lower electrode 11 is solid, is mounted on a flexible diaphragm '9, and extends within a surrounding tube 10, it being made adjustable towards and a limited distance away from the electrode 12 by means of an adjusting screw 19 threaded into the tube 10. In place of screw 19 a second screw (not shown) can engage'the female thread in electrode 11 for major retractions. The other main electrode 12 is fixedly mounted in the upper wall of the guide 1 and is made hollow to receive an auxiliary electrode 14. This is sealed into the mounting tube 20 by means of a glass bead 21. The interior of the T. R. cell is capable of being evacuated and filled with a suitable filling, if desired, through an exhaust tube 22 which is sealed off by a glass bead 23.

As mentioned above, it is required that the main gap 18 present between the tips of the main electrodes 11, 12, become ionized under predetermined conditions, i. c. When a predetermined level of ultra-high frequency energy is present in the cell in order that the gap may act as an attenuator of that energy, whilst it is not so ionised by energy having a level of below the predetermined value. To this end, a carefully controlled continuous priming ionisation is applied between the hollow main electrode 12 and the auxiliary electrode 14 mounted within it.

In order to stabilise the ionising current flowing to the auxiliary electrode 14, it is, in accordance with the invention, constructed to incorporate a resistor. The con Patented Ap 1953 struction of the auxiliary electrode may then be as shown to. The extension wire 26 may be formed of nickel while the tip 27 may be of rhodium, the tip being joined to the remainder of the electrode by welding at 28. The

ceramic resistor 25 thus forms an intermediate portion of the conductor constituting the auxiliary electrode 14, the resistor 25 having end caps 29 secured to the con- "ductor 24 and the-extension wire 26.

In order to sheath the auxiliary electrode so that the discharge thereto is confined to the tip 27 thereof, the end of the. conductor 24, the resistor 25, and the'extension'wire 26 are sheathed in an insulating sleeve 30 which may be constituted of an insulating material such as Sintox above mentioned. The sleeve 30'is secured around the appropriate portion of the auxiliary electrode by means of glass 31 which is sealed around the conductor 24 and to the adjacent end of the insulating sleeve 30. We may provide around the intermediate portion of the insulating sleeve 30 a glass bead .32 which is adapted to engage the interior of the main electrode 12 and centre it therein.

In the modified arrangement shown in Fig. 4, a somewhat sirnilar construction is employed, but in' this case the caps 29 on the ends of the resistor 25 are directly .welded and/or brazed to the ends of conductors 24 and 26 without the interposition of the sleeves employed in the arrangement shown in Fig. 3.

A further modification is shown in Fig. 5 in which one end of the resistor 25 is connected to the end of conductor 24 by means of a wire 33 which is coiled around the end of resistor 25 and then extended axially to be secured to the end of conductor 24 by welding at 34. The other end of resistor 25 is directly connected to wire 26 by coiling the end of the wire around the appropriate end of the resistor 25. In order to secure good electrical contact between the ends of the resistor and the wires to which it is connected, we may metallise the contacting portions of the wires and resistor as indicated at 35.

The Fig. 5 arrangement also shows a further modification in which the glass sheath 31 is extended to surround the portion of the auxiliary electrode including resistor 25, thus obviating the necessity for the use of a separate insulating sleeve 30. If desired, the glass sheath 31, where it surrounds the resistor 25, may be heated and caused to collapse on to the surface of the resistor, as shown by the interrupted lines.

In an alternative design the auxiliary electrode may be a wire whose sides are insulated and whose exposed tip is treated to form a highly resistive layer on to which the tip'material is fixed. For example, a wire of ironnickel-cobalt alloy maybe sheathed with glass, the end exposed by grinding, then oxidised by heating in air and then copper plated to form a protective layer on top of the oxide. The copper (preferably oxidised on the surface) forms a suitable cathode for a priming discharge operating in a T. R. cell containing water vapour and protects the oxide layer from electrochemical attack by thedischarge. The resistance value which is not critical, may be about one megohm.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high frequency electric discharge device comprising a sealed envelope, an ionisable medium filling said envelope, spaced coaxial main electrodes in said envelope, an auxiliary electrode associated with one of said main electrodes,'said auxiliary electrode being in the form of a conductor substantially completely shielded by said one main electrode fromthe other main electrode and from said one main electrode by a surrounding sleeve of vitreous material which exposes the tip of the auxiliary electrode, and a resistor incorporated in said auxiliary electrode, said resistor being in series with and close to the tip of said auxiliary electrode, said resistor being located within said vitreous sleeve.

2. An electric discharge device as claimed in claim 1, in which said one main electrode is hollow, said auxiliary electrode being located within said' one main electrode.

3. A high frequency electric discharge device comprising a sealed metal envelope of rectangular cross-section, end walls to said envelope having windows in the form of resonant slots therein,.said slots being filled with glass sealed to the rims thereof, an ionizable medium filling said sealed metal envelope, coaxial main electrodes mounted on opposite walls of said envelope between said end walls, one of said main electrodes being hollow, an auxiliary electrode mounted within and insulated from said one main electrode, said auxiliary electrode being protected with an insulating sleeve which exposes the tip of said auxiliary electrode adjacent said one main electrode, and a resistor incorporated in said auxiliary electrode so as to be in series in the path of a discharge taking place between said one main and said auxiliary electrode.

References Cited in the file of this patent UNITED STATES PATENTS 2,038,049 Kirsten Apr. 21, 1936 2,303,514 7 Toepfer Dec. 1, 1942 2,404,116 Wolowicz et al July 16, 1946 2,445,445 Marcum July 20, 1948 2,454,741 McCarthy Nov. 23, 1948 2,632,854 Altar et al Mar. 24, 1953 2,652,618 Prescott Sept. 22, 1953 

